The present invention generally relates to an integrated circuit (hereinafter abbreviated to "IC"), and particulary relates to an IC which includes a constant voltage circuit and which is required to have a low power consumption, for example, like an IC for a clock.
Conventionally, there has been a constant voltage circuit for such an IC of the kind described above, which is constituted by a reference voltage generator, a differential amplifier, a mono-channel output driver, and a negative feedback amplifier. The reason why the output driver is constituted to have a mono-channel is that it is possible to reduce the current consumption at an output driver portion by omitting an output driver on a P channel side.
In such a conventional constant voltage circuit as described above, however, there is a defect in that since no output driver is provided on the P channel side, the constant voltage output cannot be kept stable in case of occurrence of periodical fluctuations in a source voltage to thereby cause erroneous operation of the IC or deterioration in characteristics of the IC. For example, in the case of an IC, for example, for use for a clock, using a battery and having a buzzer output function, the source voltage supplied to the IC becomes small during the buzzing operation. This is because, during the buzzing operation, the current load of the battery becomes large so that the voltage drop due to the inside impedance of the battery becomes large correspondingly.
In case of occurrence of such fluctuations in power source, there occurs a phenomenon that the output of the constant voltage circuit becomes accumulatively large so that the output of the constant voltage circuit becomes impossible to converge to a fixed value and becomes larger than that in a normal condition. When the constant voltage output is used in a liquid crystal display, the contrast of display becomes so intensive in buzzing operation that deterioration of display quality may be caused. Thus, in the conventional constant voltage circuit, there has been a problem in that the output voltage of the constant voltage circuit cannot be kept stable in heavy load driving.